The present invention relates to an elastomer film produced from a thermoplastic elastomer composition by an air-cooled inflation method which is sufficiently oriented not only in an MD direction but also in a TD direction, thereby showing a small anisotropy, a method and an apparatus for producing such an elastomer film, and a microporous composite film comprising such an elastomer film.
Films made of thermoplastic elastomer compositions consisting of elastomers and thermoplastic resins have elasticity and shrinkability which are not possessed by thermoplastic resin films, so that they are expected to be used in many applications.
Films of such thermoplastic elastomer compositions containing ethylene-vinyl acetate copolymer (EVA) components are partly produced by an inflation method, but most of them are produced by a casting method. However, in the production of films by a casting method, drawing in an MD direction (longitudinal direction of a machine) is relatively easy, but drawing in a TD direction (transverse direction) is difficult, making it difficult to produce biaxially oriented films. In addition, to prevent the blocking of films, a parting sheet should be inserted into adjacent film layers in winding, posing economic disadvantages.
On the other hand, in the production of films by an inflation method, the above problems can be avoided, but since the thermoplastic elastomer composition shows a low melt tension in the production process of the films, it is difficult to keep bubbles of the thermoplastic elastomer compositions stably. Particularly, in the case of producing thin films (60 .mu.m or less, particularly 40 .mu.m or less), uniform films cannot be obtained because the bubbles are not kept stable.